Dielectric block filters are well known in the art. In general, dielectric block filters are comprised of a monolithic block of ceramic or other dielectric material, through which holes are formed, the interior surfaces of which are then plated with a conductive material. The exterior surfaces of the monolithic block are also typically coated with conductive material, with the exception of one surface of the block through which the holes within the block extend.
The coated, metallized surfaces within the holes through the block, by virtue of the physical dimensions of the block permitting an appropriate length of metallization within the hole, form quarter-wavelengths of transmission line, of which, one end of which is shorted to the metallization on the exterior surfaces of the block. These short-circuited quarter-wavelength transmission lines form resonators having relatively high Q and comprised tuned elements of a dielectric block filter.
In many applications for dielectric block filters, multiple resonator stages formed by these shorted lengths of transmission line are to be electrically connected together, typically in series with other resonator but also possibly in parallel. At the same time that such stages are to be connected together, in many applications it is desirable to electrically isolate the resonator stages from each other to reduce undesired signals in one stage from being coupled into a succeeding stage. In these applications, the resonators comprising these stages require coupling to one another, typically through either discrete lengths of wire soldered to coupling pads on the top of the block near the open circuit end of these transmission lines or by means of printed patterns on top of the monolithic block of material.
As stated above, coupling resonator stages together has previously been accomplished largely using lengths of wire or lumped inductor elements. In using a length of wire to couple resonator sections together, cross talk between the resonator stages and signals on the wires typically occurs, which can severely degrade the filter's performance. Futhermore, lengths of wire that are physically attached to connection pads on the top of the block are susceptible to physical dislocation and disconnection by virtue of the fact that the lengths of wire are exposed to the external environment around them.